When I sit to play my small Ardival Kilcoy harp, I usually sit it in my lap. It's that small. But because I am rather short, and chairs are rather tall, my thighs always slope toward the ground. This results in the harp always slowly edging its way closer and closer to my knees, until I have to interrupt what I'm doing to haul it back up. Not great in the middle of a piece.
I have tried footstools, and they help - but usually too far in the other direction for comfort. If I can wrangle a bench to perform on, I can also put the harp on it, between my legs as I straddle the bench. Then it and I are on the same plane, and stay in the same place. But I have wanted a chair I could perform in, without stacking books and magazines under my feet, as if I were a wobbly table.
IKEA's MAMMUT children's chair seems, at first blush, to be almost perfect (comical shape aside). The seat is just under 12" from the ground, 6" lower than most chairs. That's a tidge too low for me, so I lean back a little as the harp creeps higher in my lap - but the chair has a back, so that's okay! My main worry is that I am something like 4-5 times heavier than a small child, and I cannot find a weight rating for MAMMUT. One day, the harp and I may go sprawling. But for $15, I'm willing to throw a drape over it and give it a shot.
I have had a 12" porter's stool for a while:
It's the same height as MAMMUT, and looks much more SCA-appropriate (even if I can't say that the design is historical), but it doesn't have that back. I've taken it to events as a seat, and I can use it to play my larger 25-string harp (harp on ground, me on stool), but my abs can't quite handle it with the lap harp.
X-frame stools are period for me. Maybe one day I'll determine my ideal sitting height and follow these DIY instructions to make one. (There are wooden camp stools for sale, but at 18", it's back to being too high.) This stool is rather fancy; I have somewhere a source for an archaeological find of a folding Roman camp stool of wrought iron and leather... but it may still be too tall at just over 16" high, and 21 lbs is definitely not in-line with my current desire to travel light.